1. Field of the Invention
This invention relates generally to generating composite images and, more particularly, to correcting correlation errors in a composite image.
2. Description of the Related Art
The generation of composite images has many applications. One such application is the generation of panoramic images. Panoramic images can be generated from a number of separate images joined together to create a composite image that simulates a panoramic photograph of the same subject matter. For instance, a camera can be mounted on a tripod and rotated through a predetermined range of motion. As the camera is rotated, photographs may be taken periodically, with efforts to ensure that the images in sequential photographs overlap. The images in the individual photographs can then be joined to produce a panoramic image similar to what could have been acquired if a panoramic photograph had been originally taken.
One aspect of generating composite images is the alignment of the subject matter in the constituent images being joined. The subject matter of a first image must be accurately aligned with the subject matter of the second image at the seam where they are to be joined to prevent unattractive discontinuities in the composite image. This is particularly difficult in some contexts, such as when there are large periods of time between when the constituent images are captured, when there are significant variations in lighting conditions between constituent images, and where the images lack significant distinguishing features on which the alignment can be based.
One technique for aligning the subject matter in constituent images for placement in a composite image is known as xe2x80x9ccorrelation.xe2x80x9d Computers greatly facilitate correlation and a number of computer-implemented correlation techniques are known. One exemplary correlation technique is detailed in Digital Image Processing, by William K. Pratt (1991, 2d ed.) and discussed further below. However, these computer-implemented correlation techniques are also subject to problems in the contexts discussed above.
For instance, a second constituent image is frequently taken under brighter or darker lighting conditions than was the first image when the images are captured outdoors. In such situations, one may discern the seam in the composite photograph from the varied lighting conditions on either side of the seam. Another condition that may be called xe2x80x9cstutteringxe2x80x9d is illustrated in FIG. 1. Because of the lack of distinguishing features in the first and second constituent images 10 and 12, the composite image 18 includes an artifact 24 ghosting the desired image 12 and evidencing a poor correlation. Such a correlation error readily marks the seam 20, and is therefore readily detectable by the human eye, aesthetically unpleasant, and unacceptable for most uses of the resulting composite image.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.